I found out that my feet swell terribly on multi-day hikes. It usually takes about 4 days to swell up completely, but at that point my feet are 2 full sizes larger than normal. Needless to say, this resulted in some *horrible* blisters on my first Camino. I stopped off at the Decathlon in Logroño and bought new shoes that fit my swollen feet and left my old ones behind. I wore those shoes on my second Camino this year and they were fantastic all the way through. Interestingly though, my feet have only just recovered from the swelling 6 months after I finished (although I did hike the Hadrian's Wall path in August too).